Lapping machine and method of truing the lapping elements



1,634 745 July 5, 1927. W. F. FRASER LAPPING MACHINE AND METHOD OF TRUING THE LAPPING ELEMENTS Filed oct. a, 1924 2 sheets-Sheet l HIII!! Umevlofv Narren F.' F'raser wfg 1,634,745 July 5 1927' w. F. FRASER LAPPING MACHINE AND METHOD ofj TRUING THE LAPPING ELEMENTS Filed Oct. s, 1924 2 Sheets-Sheet 2 5| Fig. a

Warren F1 Fraser Ratented July 5, 1927.

UNITED Y STATES PATENT OFFICE.

WARREN F. FRASER, OF WESTBORO, MASSACHUSETTS.

LAPPING MACHINE AND METHOD OF TRUING THE LAPPING ELEMENTS.

Application llled October 8, 1924. Serial No. 742,477.

This invention relates to abrading machines and more .particularly to a lapping machine of the type shown in my copending application Serial No. 684,547 filed January 5, 1924, as well as to a method of truing the lapping elements.

A lapping machine of this type is one in which the work is ground between oppositely disposed laps mounted for movement towardsone another. The work is moved in a suitable holder located between the laps which is given a compound motion alon a continuously changing path, the parts ieing so arranged and the work so moved that every portion of the lapping surface is covered by the work at some time durin its movement, whereby the formation of ines on the work is prevented and a uniform wear of the lapping elements insured.

In machines of this type the active surfaces of the laps must approximate a g metrical accuracy, since the shape of t e laps determines the shape of the work. It is, therefore, necessa to true the surfaces of the laps periodica ly in order to insure the formation of correctly sized work. In machines of this type, as heretofore constructed, it has been necessary to remove the laps from the machine and to bring them down to the required surface in a lathe or other suitable machine, after which the laps must be remounted in the la pin machine in proper positions for the apping operation. This rocedure has involved various difficulties, 1n addition to being expensive in consum tion of time and the use of other machines or truing the laps.

It is the prime purpose of my invention to provide a construction which will ermit the laps to be trued without remova lfrom the machine; and`- It is a further object of this invention to provide a novel method of truin the laps in situ, which will insure the provlsion of an accurate surface with the minimum of attention and skill on the part of the operator of the machine.

With these and further objects in view as will be apparent in the following disclosure,

my invention resides in the combination of arts and in the steps of a process as set orth in the s ecicat1on and covered by the claims appen ed hereto.

Referring to the drawings which illustrate one embodiment of my invention:

Figure l is a vertical elevation with parts Fig. 2 is a detailed View on the line 2 2.

of Flg. l;

Fig. 3 is a detail elevation of the parts shown in Fig. 2 and;

Figs. 4, 5 and 6 are diagrammatic representations'of the relative positionsof laps and truing elements during successive stages of my method.

Fig. 7 is a partial plan view of one form of work holder mounted on its carrier; and

. Fig. 8 is a perspective view partly in section of the work holder carrier:

Referringto the drawings, I have there shown a machine base 10 on which are mounted the two annular lapping elements 11 and 12, between. which the Work is to be abraded. While these elements may be otherwise mounted for carrying -out the process herein described, I have shown the upper lappin element 11 vertically movable towards and rom the lower lap. The lower lap 12 is positioned on an annular member 14 which in turn is suitably mounted on three supporting projections 15 fixed to the base lO-of the machine, the mounting of these elements being rigid and such that the lower la 12 is held securely in position without anger of vibration or other detrimental movement.

The upper vertically movable lap is preferably carried by a post 18 slidably mounted in two bearings 19 and 20 which are suitably constructed and mounted on the frame 21 which projects upwardly from the base to a position over the lapping elements. While this post may be vertically moved by suitable opeation mechanism I have shown it in simplified form in the present case as manually movable. For this purpose the post is provided with a slot 22 near its upper portion within which rides a pin 23 projecting inwardly through the bearing 20, thus permitting vertical movement but preventing turning of the post.

bolted the carrier o the lap or the lap itself. In the present case I have shown an annular ring 30 constituting this carrier bolted to the arm 29. l

Each of the laps 11 and 12 may be made of suitable material as is Well known in this art, and may be either a Stone of sultably bonded abrasive grains such as 1s employed for grinding Wheels or it may be made of metal, such as iron. In the latter case, a loose abrasive material mixed with water or oil is employed to furnish the abrading action. As illustrated, the laps are made of vitrilied bonded abrasive grains of the grinding wheel type and may accordingly be secured totheir supports by suitable means such as a cement, sulfur, or the like.

In accordance with one phase of my invention, I propose to true the adjacent, opposed faces of the laps b means of an abrading element 31 placed t erebetween and suitably moved to grind the faces of the laps until they lie in parallel planes. This truing element may be made of abrasive material similar to the lapping elements or it may be ofmetal and used with an abrasive powder or-compound for the abrading operation. I prefer to move the truing element between the laps through a path which does not repeat itself for many c cles, and thereby prevent the formation o ring markings.

One problem involved in truing the laps lies in the fact that the intermediate truing element may not have faces which are exactly parallel with the desired planes of the laps. As illustrated in an exaggerated fashion, in Fig. 4, this truing element may be .somewhat conical in shape and so tend to form the laps with tapered faces. In accordance with my invention, I propose to4 use such a truing element without providing it with accuratel shaped faces and to carry out the metho in such a manner that any verror is automatically rectified. I accordingly abrade the lappinoI faces with such crudely formed truing element until the laps and the truing element have attained a uniformity of surface and the adjacent surfaces of each lapand the truing .element are substantially parallel. Thereafter I remove the truing element from theI machine and turn it bottom side up and again resume the truing operation. As shown in exaggerated form in Fig. 5, the

.truing element will be lar ely out of con-- tact with the laps but a er moving `the truing element through its grinding cycle for a time, it will be found that the truing element and the laps have worn each other away and the la s have now ap roached'a more nearly per ect condition. y reversv ing the truing-element one or more times thereafter, I may bring the laps finally to a condition in which the lap surfaces are substantially parallel planes.

In order to give the truing elements a suit-able motion for carrying out my method, I may employ the construction illustrated in my copending application or as shown herein in simplified form. As illustrated,

I provide a shaft 32 suitably mounted in bearings on the machine which is rotated by a pulley 33 or other proper drivmg mechanism. A sleeve 34 surrounding the shaft 32 is also mounted for rotation thereabout, the upper end of this sleeve carrying a collar 35 which bears against the cen- In order to give the work or the truing element the desired compound rotary move-- ment, I form the shaft 32 with an enlarged head 40 having an exterior cylindrical surface eccentric with the shaft. A split collar 41 is clamped on this cylindrical head and may be suitably adjusted in position by loosening a clamp screw and revolving the collar about its center. A driving pin 43 is mounted in a socket in the collar with its axis eccentric to the center of the head 40.

`This head is also so positioned that as the collar 41 is adjusted about the head 40, the pin may be brought into axial alignment with the shaft 32 or by revolving it further 'around the center of the head, it may be given the maximum eccentricity as shown in the drawing. By means of this adjustment,

I may vary the throw or radius of movei plained, this yoke member 46 which is given the compound movement is left normally in place when the work or the truing element is removed and it is merely necessary to drop the work carrier or theplate 44 over this yoke member in proper position to permit the lapping and truing operations.

It will be seen, so far as now described, that rotation of the-pin 43 will carrythe center of the truing element about a circle of small radius. In order to give this holder 44 a rotary motion aboutl its center as it relio volves, I provide a connection between the plate 44 and the sleeve 34 which is meant to rotate at a slower speed than the inner shaft 32. The collar has an outwardly projecting crank arm 50 which has an up-turned portion 5l provided with a hole therethrough. Connection is made between this arm 50 and the driving plate 44 through a separate member comprising a horizontal plate 52 which has a pin 53 projecting upwardly at one end and another pin 54 projecting downwardly at its opposite end. The pin 54 fits. rotatably Within the hole in the portion 51 of the crank arm and the pin 53 is likewise adapted to be pivotally mounted in a hole 55 in the u wardly projecting pin 56 of the drivingr yo (e 46 which inturn fits within a hub in the place 44. Cover plates 57 over the upper ends of the holes in the hub of the yoke 46prevent admission of abrasive to the bearing pins 43 and 53.

It Will therefore be seen that when the shaft 32 and the sleeve 34 are rotated at different speeds, the first rapidly and the second slowly, the plate v44 and consequently the truing element 3l will be rotated slowly about its center While the center is revolved at a rapid rate. These two movements cause the truing element to be carried around in a rapid loop-like motion while it travels about the axis of its .driving shaft. These motions are so timed and related that the abrading or truing element and the laps are moved relatively in a compound nonrepeating path; that is a given spot on the truing element does not travel in the same path on a lap until it has been revolved many times. This insures even wear of the laps. It, however, will be understood that the driving mechanism may be suitably con structed to give any desired movement so far as the broader aspects of my invention are concerned. ItV will also be understood that by adjusting the pin 40 in its -collar 41, I thereby vary the extent of the loop-like motion of the truing element relative to the laps. If the pin 43 is axially aligned with the shaft 32, the element 31 will then be given a simple movement of revolution about the center line of the laps. Also, it will be understood vthat it is feasible within the broader aspects of my invention to move the laps instead of the central abrading element to true the laps, it being merely necessary to provide a relative movement therebetween.

It will be understood that the abrading element is employed `only when necessary to true the lap faces. During the normal operation of the machine, the abrading element 1s replaced by a Work holder. The carrier for the work holder fits over the driving pms 43 and 53 and is arranged to move. the Work through the same path as that given to the abra ing element. The work carrier as shown in Figs. 7 and 8 ma comprise a plate 60 having an annular ange 61 arranged to hold the removable disk shaped work support 62 in position. The latter may rest on the plate 60 and be keyed theref to by keys 64 so that the parts will revolve together. The carrier 60 has a boss 65 projecting therefrom which is provided with openings into which the pins 43 and 53 project, these being so arranged that pin 53 is concentric with the carrier and pin 43 eccentric relative thereto. The work holder 62 which is thinner thanthe distance between the laps may be provided with holes 66 of suitable shape to fit the work pieces to be treated.

The operation of thev device and of my method will be apparent in view of the above explanation, and it will also be obvious that various modifications may be made therein within the .scope of the appended claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patenis:

l. The method of truing two opposed lap faces to bring them into arallel planes comprising the steps of re atively movin an abrasive element of wearable material aving extensive plane surfaces between and in cont-act with said lap faces to abrade the same, reversing said element and repeating the abrading operation upon the laps with said element in its reversed position.

2. The method of truing the two opposed surfaces of flat laps to bring them into parallel planes comprising the steps of moving an abrading element of wearable vabrasive material, which has a plane face contacting with each of the laps, in a compound nonrepeatin path relative tothe laps so as to abrade t em, reversin said element-so that each lap surface will e acted upon by that face of the abrading element which formerly contacted with the other lap, again abrading the laps thereby, and repeating the cycle of abrading and, reversal until the surfaces f the laps are parallel and true planes to a high degree of accurac 3. The method of truing the opposed surfaces of flat lapping or abrading elements to bring them'into highly accurate parallel planes comprising the steps of introducing a third element, having extensive lplane faces, between said lap faces and causlng a relative lapping movement between them whereby the face of each lap and the contacting faces of said third element, are each abraded until they have extensive surfaces in contact, reversing the third element and repeatin the lapping 'movements until the said sur aces are again in extensive contact, and repeating said process until the desired degreeof accuracy of plane. and parallelism is obtained.

i4. A device for truing the opposed faces of the lapping elements in a lapping machine having two laps with opposed disk faces and including mechanism to cause relative movement between the laps and work placed therebetween to lap said work, comprising a removable element having extensive plane faces which are capable of abrading said lap faces simultaneously and means whereby said element may be mounted between the said laps and moved by said mechanism to true the laps.

5. A device for truing the opposed faces of the lapping elements in a lapping mlchine having two laps with opposed disk faces, comprising a wearable abrading element having plane faces, means removably supporting said element with its faces between and in contact with the laps, and means to move said element and the laps relative to each other in a compound nonrepeating motion to abrade the laps, said parts being so constructed and arranged that the laps may be repeatedly abraded, each first with one face of said element and then with the other, and their faces ultimately brought into parallelism.

6. A device for truing the opposed faces of the lapping elements in a lapping machine having two laps of abrasive material with substantially .parallel opposed disk faces, and having means to mount and ro.- tate a carrier therebetween in a compound non-repeating motion, comprising an abrading element of disk shape, means for removably mounting the abrading element on said carrier with its plane faces contacting with the two lap faces andso arranged that it may be reversed and means permitting the laps to bear against said element and be trued bythe rotative movement of the carrier.

Signed at Worcester, Massachusetts, this 6th day of October, 1924.

A WARREN F. FRASER. 

